There are many instances where it would be useful or desirable to provide a computer readable form of a document not available in a compatible computer readable form. Normally it is the case that the document is not available in machine readable form because the document was handwritten or typewritten and thus no computer readable form exists, or because the computer readable form is not available. In some instances there is a "foreign" document, i.e. an existing computer readable form but the document was produced on an incompatible computer system. In some instances, such as facsimile transmission, a simple optical scan of the document can produce the required form. In most instances the form most useful for later use and decision making is a separate indication of each character of the document.
The field of optical character recognition deals with the problem of separating and indicating printed or written characters. In optical character recognition, the document is scanned in some fashion to produce a electrical image of the marks of the document. This image of the marks is analyzed by computer to produce an indication of each character of the document. It is within the current state of the art to produce relatively error free indication of many typewritten and printed documents. The best systems of the prior art are capable of properly distinguishing a number of differing type fonts.
On the other hand, unconstrained handwritten characters have not been successfully located and recognized by present optical systems. The problem of properly reading unconstrained handwritten characters is difficult because of the great variability of the characters. One person may not write the same character exactly the same every time. The variability between different persons writing the same character is even greater than the variability of a single person. In addition to the variability of the characters themselves, handwritten text is often not cleanly executed. Thus characters may overlap horizontally. Loops and descenders may overlap vertically. Two characters may be connected together, strokes of one character may be disconnected from other strokes of the same character. Further, the individual written lines may be on a slant or have an irregular profile. The different parts of the handwriting may also differ in size. Thus recognition of handwritten characters is a difficult task.
An example of a field where recognition of handwritten characters would be very valuable is in mail sorting. Each piece of mail must be classified by destination address. Currently, a large volume of typewritten and printed mail is read and sorted using prior art optical character recognition techniques. Presently, approximately 15% of current U.S. mail is hand addressed. Present technology uses automated conveyer systems to present these pieces of mail, one at a time, to an operator who views the address and enters a code for the destination. This is the most labor intensive, slowest and consequently most expensive part of the entire mail sorting operation.
Furthermore, it is expensive to misidentify a ZIP code and send the piece of mail to the wrong post office. Once the mail is forwarded to the receiving post office, the receiving post office recognizes that there is no matching address or addressee in that ZIP code. The mail must then be resorted and redirected to the proper post office. Because of the high expense associated with misdirected mail, it is more desirable to have an automated system reject a piece of mail if the system cannot determine the ZIP code with an extremely high degree of accuracy. The rejected pieces of mail can then be hand sorted at the sending station or other measures can be taken to eliminate or reduce the cost of the misdelivery.
Sorting of handwritten mail is an area having a unique set of characteristics. First, due to the problem of user acceptance it is not feasible to place further constraints on the address. Thus address lines or individual character boxes, which would be useful in regularizing the recognition task, are ruled out. On the other hand, there already exists a relatively constrained portion of the current address. The ZIP code employed in a majority of handwritten destination addresses provides all the information needed for the primary sorting operation. Most handwritten ZIP codes are formatted with 5 digits while some handwritten ZIP codes use the longer 9 digit ZIP code. This information is relatively constrained because the ZIP code consists of only 5 or 9 digits. In addition the ZIP code is usually located at the end of the last line of the destination address or sometimes is by itself on the last line.
Various systems have been devised to recognize handwritten digits. However, many of these systems assume that the digits are already located and isolated and the problem is only to determine which numeral the handwritten digit represents. Often these systems require the digits to be written inside individual boxes.
In order for a computer to analyze and recognize the handwritten numerals in a hand-written ZIP code in an address block typically appearing on an envelope, the group of numerals comprising the ZIP code must first be successfully located as a group.
Even though the above mentioned constraints on the ZIP code in the form of number of digits and location exist, previous attempts to locate the ZIP code have encountered problems. The same problems that exist in general for successful recognition of handwriting also pose problems for locating the ZIP code. Previous attempts to count lines of a handwritten address block have been stymied by loops, descenders, line slant or other line irregularities.
What is needed is a highly reliable system to correctly locate the ZIP code in an address block before analysis of the digits of the ZIP code.